I have read few of your posts before and my perspective is that whatever dynamic your mother has with your brother and sis-in-law should be addressed head-on by her. Time has come for your mom to directly or indirectly let your brother know that this time it is actually her decision to move to a different country with you and not a necessity or circumstantial. That may make your brother and his wife also think what prompted her to make that call and they may improve their relation with your mom. After-all location wise your mom is better is off with your brother and after you guys settle down she can visit you guys often in the new country. You should neither be be feeling guilty of separating your mom and brother nor put her in a tough environment which she does not fully realize about. I mean, even people in 20's and 30's get lost and feel alone when they move to a new country as dependents with their spouse etc..